Application And Electrochemical Properties Of Self-standing Interlayer In Lithium-sulfur Battery

Lithium-sulfur battery,using sulfur as the cathode and lithium metal as the anode,is the most promising energy storage devices because of the high theoretical energy density of2600Wh/Kg.But the practical application of lithium-sulfur battery is greatly limited by several problems:?1?low conductivity of elemental sulfur and volume expansion during circulation;?2?shuttle effect of lithium polysulfide;3)lithium dendrites and problems of safe using.These factors can seriously affect the electrochemical property of Li-S batteries,thereby limiting the industrialization of lithium-sulfur batteries.Therefore,the preparation of a material excellent in electrical conductivity and capable of suppressing dissolution of polysulfide has become a key point of research.This paper focuses on the inhibition of polysulfide dissolution and electrical conductivity properties,the preparation of composite cathode and interlayer new structure in order to improve battery cycle stability and battery capacity.The research content of the thesis is three parts.1)Super P,activated carbon?AC?and vapor-grown carbon nanofibers?VGCF?are three kinds of carbon materials with different morphological structures.The authors prepared three kinds of carbon interlayers by using SP,AC and VGCF and lithium-sulfur batteries with carbon interlayer and sulfur cathode were made to compare the effects of different morphology carbon interlayers on the cycle stability and capacity of batteries.The results show that the performance of lithium-sulfur battery using the carbon materials interlayers improved.The electrochemical performance of VGCF interlayer is the best,the initial discharge capacity of which is 1262 mAh/g at 0.1 C.The capacity of it remains 912mAh/g after 100 cycles and the capacity retention rate is 73%.2)CoS₂ particles was prepared by hydrothermal method and CoS₂/S composite was made by solvothermal method.Then the electrochemical properties of CoS₂/S-VGCF interlayer and S-VGCF interlayer was compared to study the effect of CoS₂ particles on the cycle stability of lithium-sulfur batteries.The results show that the discharge capacity and cycle stabilit of CoS₂/S-VGCF interlayer are high than that of the S-VGCF interlayer.The initial discharge capacity of the CoS₂/S-VGCF interlayer at 0.1 C is 1278 mAh/g and the battery capacity is as high as 701 mAh/g after 200 cycles,which is 149 mAh/g high than the S-VGCF interlayer?100 cycles?),with Coulomb efficiency is close to 100%.3)Polypyrrole?PPY?was formed on the surface of vapor grown carbon fiber?VGCF?by in-situ deposition to prepare VGCF/PPY and then VGCF/PPY interlayer was prepared.The electrochemical performance of CoS₂/S-VGCF interlayer and CoS₂/S-VGCF/PPY interlayer were compared to explored the advantages of chemical adsorption and physical adsorption combined with inhibition of the shuttle effect.The results show that the discharge capacity and cycle stability of CoS₂/S-VGCF/PPY interlayer is excellent.The first discharge capacity of the CoS₂/S-VGC/PPY interlayer at 0.1 C is 1278 mAh/g,the battery capacity is maintained at 1262.48 mAh/g with the coulombic efficiency of 100%even after 300 cycles.The initial discharge capacity of CoS₂/S-VGCF/PPY interlayer at 0.5 C is 1066.42mAh/g,the battery capacity is maintained at 854.71mAh/g after 300 cycles and the capacity retention rate is 80.14%with the ultra-low capacity attenuation of 0.066%per cycle.It shows that the CoS₂/S-VGCF/PPY interlayer maintains good cycle stability with different currents.